1. Field of the Invention
The present invention relates to an inkjet recording method that enables formation of images of good fastness, high density and good glossiness.
2. Description of the Related Art
These days the mainstream of image-recording material is for forming color images. Concretely, inkjet recording material, thermal transfer image-recording material, electrophotographic recording material, transfer silver halide photographic material, printing ink, recording pens and others are much utilized.
In these color image-recording materials, used are three primary colors (dyes, pigments) for a subtractive color process for reproducing or recording full-color images. At present, however, few dyes are available, which have absorption characteristics capable of realizing any desired color reproduction range and which are fast under various service conditions, and it is much desired to improve colorants.
An inkjet recording method has become much popularized and is being further developed, since the material cost is low, it enables high-speed recording, it does not give too much recording noise, and it facilitates color recording.
The inkjet recording method includes two types, a continuous type of continuously jetting ink drops, and an on-demand type of jetting ink drops according to image information signals. For jetting ink drops according to the method, employable is any of a system of applying pressure to ink drops by using a piezoelectric device to thereby make the ink drops jet out, a system of thermally bubbling ink to jet the ink drops, a system of using ultrasonic waves, or a system of sucking and jetting ink drops by electrostatic force. Ink for inkjet recording includes aqueous ink, oily ink and solid (hot-melt) ink.
Colorant to be used in such inkjet recording ink must satisfy the following requirements: its solubility or dispersibility in solvent is good; it enables high-density recording; its hue is good; it is fast to light, heat, active gas in the environment (e.g., NOx, oxidizing gas such as ozone, SOx); it is fast to water and chemicals; it well fixes in image-receiving material and hardly bleeds out; its storage stability in ink is good; it is not toxic; its purity is high; and it is inexpensive and is readily available. However, it is extremely difficult to seek such colorant that satisfies all these requirements on a high level. In particular, the requirement which the colorant is strongly desired to satisfy is that it has a good hue of any of three primary colors and is fast to light, moisture and heat, especially to oxidizing gas such as ozone in the environment while printed on an image-receiving material that has an ink-receiving layer with porous white inorganic pigment particles therein.
Heretofore, azo dyes have been widely used for magenta dyes, of which the coupling component is any of phenols, naphthols or anilines. Azo dyes disclosed in JP-A 11-209673 and Japanese Patent No. 3,020,660 have good hue, but are problematic in that they are not fast to light. To solve the problem, Japanese Patent Application No. 2000-220649 discloses dyes that have good hue and improved lightfastness. However, the dyes disclosed in these patent publications are not fast to oxidizing gas such as ozone.
Typical examples of cyan dyes are phthalocyanine dyes and triphenylmethane dyes. Phthalocyanine dyes are most widely used, and their typical examples are C.I. Direct Blue 86, 87 and 199. As compared with magenta and yellow dyes, they are fast to light but are greatly discolored and faded when exposed to nitrogen oxide gas which is much discussed these days for environmental problems, or to oxidizing gas such as ozone.
JP-A 3-103484, 4-39365 and 2000-303009 disclose ozone gas-resistant phthalocyanine dyes, which, however, are still unsatisfactory in point of their fastness to oxidizing gas and are therefore desired to be further improved.
On the other hand, triphenylmethane dyes such as typically Acid Blue 9 have good hue but are not fast to light and ozone gas.
As yellow dyes, heretofore used are azobenzene dyes such as typically Direct Yellow 86 and 120, and heterocyclic azo dyes, for example, pyrazolonazo dyes such as Acid Yellow 17, and pyridonazo dyes. In addition, quinophthalone dyes are often proposed. Of those conventional dyes, quinophthalone dyes have good hue especially in point of the tailing profile on the long wave side in the absorption spectral pattern but most of them are not fast to ozone and light, while azobenzene dyes are fast to them but their tailing profile on the long wave side is not good. To that effect, dyes satisfying the two requirements of good hue and good fastness are not available at present.
For obtaining fast full-color images of good color reproducibility, dyes to constitute the images are desired to satisfy the following requirements:    Dyes of three primary colors all have good absorption characteristics.    Dyes of three primary colors are optimally combined to realize a broad color reproduction area.    Dyes of three primary colors all have high fastness.    The fastness of dyes is not worsened through interaction thereof.    Dyes of three primary colors are well balanced in point of their fastness.
However, there is no report at all relating to the fastness of dyes to oxidizing gas such as ozone, which is discussed these days as a serious problem in the art of inkjet printing, especially relating to the properties of dyes as to what structures and what properties of dyes are effective for ozone fastness thereof. At present, therefore, it is not possible to obtain a guideline for selecting dyes. Further, it is extremely difficult to select dyes that are fast to light as well.
Even though dyes of good ozone fastness are combined and used in forming full-color images, the images formed will be discolored if the combined dyes differ too much in point of their ozone fastness. Therefore, it is a matter of importance that the combined dyes, especially the combined magenta and cyan dyes are well balanced in point of their ozone fastness. If so and even when the full-color images formed are attacked by ozone, the constitutive dyes may be faded while being well balanced in point of the degree of fading of the individual dyes, and, as a result, the images may be prevented from being fatally damaged.
Depending on the type of the mordant to be combined therewith, dyes may be excessively flocculated to lower the density of the images formed. An inkjet recording method is therefore desired that enables formation of images of good fastness, high density and good glossiness.